It has been a long known practice to ventilate attics under gable roofs by running a vent along the roof ridge. Such vents are created during construction by sizing the uppermost row of sheeting panels to leave an open slot running along the ridge essentially the length of the roof. The slot creates effective heat ventilation by convection flow and suction caused by wind across the roof ridge.
Soffit ventilators are perforated or louvered openings in the underside (soffit) of the eaves of an overhanging roof. The vents allow fresh ambient air to flow into the attic to equalize attic temperature and pressure with the outside. This equalization inhibits moisture from condensing on insulation and wood roofing materials which causes mildew and rot, prevents build-up of ice dams which could buckle shingles and gutters, and reduces air-conditioning costs when hot attic air is replaced by cooler ambient air.
A soffit ventilation system works in conjunction with a ridge vent to provide passive ventilation. As hot stale air is withdrawn from the ridge slot vent by convection and/or wind suction, it is replaced by fresh ambient air through the soffit vents.
Differences between the various types of ridge vents have been primarily in the capping structures used over the vent slot to exclude water and pests. Early capping structures were often metal hoods, or "ridge caps", extending wider than the slot and having some combination of baffles and screens to exclude water and insects. Representative examples may be seen in U.S. Pat. Nos. 2,214,183 (Seymour) and 2,160,642 (Bumpas). More advanced ridge caps have used, louvers, as seen in U.S. Pat. Nos. 3,683,785 (Grange) and 4,558,637 (Mason).
Other capping structures place some type of porous material over the slot, which is then covered by the same roofing material as the rest of the roof, such as shingles or tiles. For example, U.S. Pat. No. 3,949,657 (Sells) shows using a matrix of either molded plastic or corrugated cardboard dipped in epoxy as the porous material, with shingles nailed over the matrix leaving the side edges open to vent hot air. The relatively large size and straight line orientation of the pores in this corrugated material apparently permitted wind-driven rain to back flow into the slot, as it has since been found an improvement to include a metal flashing strip with small vent holes at least on the windward side (U.S. Pat. No. 4,843,953, again Sells). Essentially similar is the corrugated polyethylene sheet material shown in patent 4,803,813 (Fiterman).
Materials having smaller and more convoluted air passages than the corrugated materials provide a more effective barrier against wind-driven water and small insects. Non-woven fiber mats and open-cell plastic foam are inexpensive materials of this description which have been used in roof ventilators. In U.S. Pat. No. 4,325,290 (Wolfert), a non-woven fiber mat is used as a filter in a vent cap system. In U.S. Pat. No. 4,942,699 (Spinelli), a thin non-woven fiber sheet is bonded to matting of nylon filaments to provide sufficient structural resilience to allow the sheet to be used under shingles. In U.S. Pat. No. 4,876,950 (Rudeen), two strips of open-cell plastic foam are joined to an impermeable plastic membrane again two parallel for use under shingles.
It is apparent from the above that inventions in the field of roof ridge vents have largely evolved from the availability of new materials, and the ingenuity of inventors in adapting such materials for venting. Without attempting to provide a exhaustive listing of desirable properties, it can generally be observed that a venting material must be sufficiently air-permeable to provide heat ventilation, but still prevent the entry of small insects, dust, and water. Consequently, materials having small convoluted air passages and non-wicking characteristics, such as non-woven fiber sheets and open-cell foam, are good candidates. But such materials should also demonstrate other mechanical and chemical properties such as tensile strength, resilience, ability to be transported in rolls and cut to length, ease of joining strips, and long term durability in local ambient conditions.
With prior vent systems, as described above, these additional properties have been achieved by laminating fiber sheets or foam strips to other materials, such as nylon matting (Spinelli) or plastic membrane (Rudeen). However, such composite materials frequently compromise some features in order to achieve others. For example, the lamination of nylon matting to the fiber sheet, as described in the Spinelli patent, gives the sheet a needed thickness and resilience, but complicates its ease of application. When the laminated material is unrolled for installation, the nylon matting must be cut back from the edge at the ends and sides, and the non-woven fiber sheet wrapped up around the sides of the matting to create a barrier against water and insects. To join two strips of the laminated material, the nylon matting must also be cut away on one sheet, and the two sheets then lapped and joined by adhesive. Moreover, even though the matting is bonded to the sheet on either side of a central hinge line, it is possible for workmen unfamiliar with the material to install it upside down; that is, with the sheet side over the matting, instead of underneath it. The potential for this error can be seem by comparing the nylon matting laminated material (Spinelli) to the plastic membrane material (Rudeen); the former is installed with the nylon matting side down, while the later is installed with the plastic membrane up. A worker experienced with only one of these materials could easily be led by his experience to install the other inverted.